MIL-HDBK-1003/11
per brake horsepower (bhp) (1.8 to 2.2 liters per second per kW).
Two-stroke engines require approximately 4 to 5 cfm per bhp (2.5 to 3.1
liters per second per kW).
5.4.8 Precooling and Aftercooling. Precooling of intake air is not
allowed. Aftercooling, sometimes referred to as "intercooling" of intake
air after turbocharging is desirable. Sufficient coolant should be made
available at the required temperature. Standby/emergency duty and prime
duty generator units may utilize separate electric motor driven pumps;
however, engine-driven pumps are preferred, with standby motor-driven pumps
available.
5.4.9
Engine Exhaust Systems.
5.4.9.1 Exhaust Silencers. Heat recovery silencers should be considered
for all prime duty installations. Recovered heat can be used for space
heating. When residual fuel oil is to be used in Design 2 and 4 plants (see
Table 1), it may be heated using hot water from heat recovery silencers.
Refer to Section 4 for additional guidance on exhaust heat reclamation and
cogeneration potential.
5.4.9.2
Exhaust Gas Quantities. Exhaust velocities and pressure drops
should be selected to match engine requirements as provided by the engine
manufacturer. Whenever manufacturer's data is not available, base system
and piping component sizing on approximately 8.4 cfm of exhaust per bhp (5.3
liters per second per kW) for four-stroke engines and on 13 cfm per bhp (82
liters per second per kW) for two-stroke engines.
5.4.9.3 Exhaust Connections. The use of flexible connections at
connections to the engine exhaust outlets or turbocharger exhaust outlets
should be included to eliminate excessive structural stresses on those
exhaust system movement, and expansion and contraction due to heat, must be
considered and provided in the plant design. Silencers should be mounted
outside the building as indicated on the Definitive Design Drawing operating
floor plans, unless the manufacturer's standard unit is provided with an
attached silencer or other special design considerations dictate otherwise
at a specific site.
5.4.10 Cooling Systems. Decide by economic analysis and site conditions
whether radiator, cooling tower, or a natural circulating water system
should be used. Where cooling systems are subject to freezing temperatures,
cooling systems must be protected during operation and when shut down.
Freeze preventing solutions (such as glycol or Dowtherm) should be
considered for circuits exposed to freezing outdoor ambient temperatures.
In severe freezing conditions, it is desirable to separate the interior and
exterior circuits by means of heat exchangers in addition to the use of
antifreeze solutions. When these solutions are used, equipment and piping
will require care in design and selection due to the lower specific gravity
(and specific heat) of the antifreeze solutions as compared to water.
Higher pumping rates will require larger piping systems and more heat
exchange surface areas. Refer to the engine manufacturer for their specific
recommendations relative to jacket coolant and lubricant cooler temperature
control and fluid requirements.
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